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davidgsmith

Running On

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I have had my engine rebuilt with a fast-road engine and it seems to run-on almost everytime I turn the engine off.

 

Can anyone help with this? I have had conflicting reasons, including timing, modern fuels etc..

 

How do I get rid of this embarrassing symptom??

Thanks

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I have had my engine rebuilt with a fast-road engine and it seems to run-on almost everytime I turn the engine off.

 

Can anyone help with this? I have had conflicting reasons, including timing, modern fuels etc..

 

How do I get rid of this embarrassing symptom??

Thanks

 

 

 

Hi David,

 

Whats your tick over rpm at idle?

 

Cheers

Guy

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David

Could you tell us more about -

your carbs, waht type and how you set mixture.

fuel pump: electrical or mechanical?

anything done to the head?

Running temperature?

All these thigns could have some bearing on the problem, and knowing a little more could help to zoom into the right answer a little quicker.

 

 

Mike

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Hi Mike,

I am on standard twin SU H6s with K&N filters, standard mechanical fuelpump (repro, with no priming lever). The head was modified Stage 2/3, gas-flowed and converted to unleaded. Temperature runs normal.

Hope this helps?

Thanks

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Hi David,

 

Running on can often happen and manufacturers used to fit anti-run on devices to their petrol engines, so you are not alone in this problem.

 

The running on is caused by a hot spot inside the combustion chamber which then ignites the incoming fuel and air.

 

As your engine has had a bit of tuning done to it, the plugs may now be running a bit too hot. So as a first step I would try a cooler grade of plug and see what happens. In the above I take it that the timing is correct.

 

Steve

iz7onc.jpg

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Hi David,

 

Running on can often happen and manufacturers used to fit anti-run on devices to their petrol engines, so you are not alone in this problem.

 

The running on is caused by a hot spot inside the combustion chamber which then ignites the incoming fuel and air.

 

As your engine has had a bit of tuning done to it, the plugs may now be running a bit too hot. So as a first step I would try a cooler grade of plug and see what happens. In the above I take it that the timing is correct.

 

Steve

iz7onc.jpg

Click on thumbnail

 

 

Hi Steve, yes I have just had it tuned so assume everything is as it should be.

When you say a "cooler" plug, what would you recommend and where from?

Cheers

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Hi David,

 

I can't make any definitive recommendations as I have not needed to play about with TR4 spark plugs, however if you are using NGK BP6HS spark plugs (standard) at present then a BP7HS would run cooler.

 

You should be able to buy these plugs from most car accessory shops it is just knowing what you want.

 

Steve

iz7onc.jpg

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Fit an anti-run-on valve, which will dump air into the inlet manifold when the ignition is turned "off". Obtainable from Moss (Code YR11933 a few years ago), but also from motor factors, where they might be cheaper. These valves come in various configurations - I have one mounted to a bracket attached to one of the head studs, and it dumps into the inlet manifold at the place where one might connect a hose to a brake booster (completely unnecessary piece of equipement on a TR!). A connection to the ignition circuit is all that is required to operate the valve when the ignition is turned "on" - this closes the valve all the while that the ignition is energised.

 

Also, when you want to stop the engine, put it in 1st gear (handbrake "on"!), bring the clutch to the point where the engine starts to slow, then turn the ignition "off". The drag from the clutch should stall the engine. I use this technique in conjunction with the anti-run-on valve.

 

In modified engines, where the head has been worked, it is necessary to trim the head gasket so that it doesn't protrude into the combustion chamber, as any such protrusion will create a hot spot, leading to running-on. it is easier to do this trimming on a solid copper gasket than on the standard gasket.

 

Ian Cornish

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Dear Dave,

 

You're miles from being alone on this.

 

When purchased, my 4A had been rebuilt as a "race" motor, with silly cam, silly advance curve, and carbs matched. Aluminium "race" radiator, with the original cowl and fan. It was all but undriveable on the road, and ran on something shocking.

 

So I pulled the cam and had it reground. While the head was off I had it overhauled and fitted with hard seats for unleaded fuel. I put it back together and it ran on really strongly. It also pinked really badly. So I had the advance re-mapped, then spent a fortune on dyno tests and an eternity making carb needles until the dyno confirmed that the needles were right. For what it's worth, my ideal result was so close to the standard "lean" needles, that it didn't matter. It still ran on.

 

The running on is temperature related. If the temp gauge is in the first quadrant, ie; not quite up to temp, it will stop when the ignition is turned off. If the needle is in the second quadrant it may or may not run on, but if the needle is above half it has to be stalled. I use top gear, it's gently on the mechanisms. The car also overheats frantically at the slightest opportunity in traffic or in warm weather, so I have fitted the biggest thermatic fan I could squeeze in there. That solves the overheating problem.

 

Compression is fine, 155PSI in each hole, so excess compression is not the culprit.

 

I tried running cooler plugs at one stage. This was in fact successful, to the extent that I tried it. Unfortunately it made the bloody thing absolutely undriveable until it was on the verge of overheating anyway. That's why some race bikes use warm plugs to start, and change to cold plugs for a race.

 

As I see it, there are only two possible causes for my problems. Either I have a wrong head gasket, perhaps to standard bore when I may have large bores from the "race" rebuild, so that I have a ring of hot spots in each chamber, or which restricts water flow through "wrong" holes, or I have a clogged water jacket. Either way, taking the head off will prove it. That's the next job, but it won't happen until August at best.

 

After that I will look at air valves, but they should not be needed if everything else is right.

 

cheers,

JFerg

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I have had my engine rebuilt with a fast-road engine and it seems to run-on almost everytime I turn the engine off.

 

Can anyone help with this? I have had conflicting reasons, including timing, modern fuels etc..

 

How do I get rid of this embarrassing symptom??

Thanks

 

Hi Dave,

Have had this problem with my similarly tuned car. No problems when I use Shell Formula 1 fuel though!

Regards,

Monty.

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How do the plugs look after a hard run?

 

andy

 

 

Hi Andy, form what i remember, they look sooty but the tip is clean and sandy coloured.

 

Monty, I will try Shell next time I fill up

Edited by davidgsmith

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I had the same problem but running the car on Avgas solved it straight away.

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That's really helpful - if you are in Australia ! :)

 

Or you know someone who flies a light plane. Proper leaded 105+ octane at every small aerodrome, just not cheap :blink:;)

Stuart

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I've been running mine on 98 octane premium unleaded, and it seems to make a slight difference over plain pump stuff which is 92 octane I think.

 

There is a caution to apply though. My previous TR4A ran standard ULP, and one day I decided to give it a treat of premium. Now apart from the octane rating, the other big difference between standard ULP and the premium is that the latter is full of aromatics and detergents. It's designed to keep modern, metric, fuel injection systems clean.

 

The former dissolved all of my rubber fuel lines from the filler neck down, the latter released 40 plus years of deposited crud. I bought fuel filters by the gross and was quite adept at changing them..... every time the car stopped.

 

So the new 4A had all those bits changed when I got it.

 

cheers,

 

JFerg

Edited by JFerg

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doesn't solve the root cause, but pressing on the gas pedal after turning off the ignition sends a squirt of fuel into the cylinder that cools it and stops the run on. I had a TR3 that did this and this worked well. Hurts the MPG though!

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Hi David,

I'm on a standard 4a set-up that has done about 15k miles since total professional rebuild including unleaded conversion ............ and it used to run on something awful pretty much every time.

 

My local TR guys advised the SU's were worn to the extent they weren't closing off fully at switch-off and so were permitting fuel mix to still pass through, and were also making it difficult to get a nice steady slow-enough tickover. These 2 combining to encourage the engine to continue in the absence of myself and keys!! I invested in a pair of brand new SU's, not cheap I know, but this solved the problem by 95%. Cost was justified on the "never ending hassle factor".

 

Re hotspots ..... I agree with the previous postings......before I switch off nowadays I always just check the temp gauge .......if it's showing below two thirds I switch off with no run-on. If it's showing two thirds or above I know from experience it may well run-on .......so I turn on the electric fan for a minute before switch-off - and she stops with no run-on. Not sure if that's coincidence - but it works for me !! Try it ?? :)

 

Cheers,

 

Mikell.

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I have a standard 4A engine, new(ish) SUs, standard needles (TW). Temp needle is always rock solid centre of gauge. On a hot day with 95 RON there is a slight chance of run on. With 98 RON and Castrol octane boost, never.

 

A while back I had a slight leak air leak on the inlet and was running a bit lean. This caused run on. I have also had a partially blocked fuel filter causing (in effect) a weak mixture. This caused run on.

 

Andy

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My running on after purchase stopped after a re-time and tune according to the manual.

 

 

 

My own experience matches Little Jim's. State of tune affects the problem, with the 4 set up and tuned to within an inch of its life it runs on, backing off on the verier just a degree or two so that it just burps (sorryblink.gif ) is enough to solve the problem whilst maintaining the higher level of tune.

 

Seems like everybody has a different solution to (probably) different root problems.........................try all the solutions until you find the one that matches YOUR root problemwink.gif

 

PS: Ref early post, always run LNK on 98, 99RON if I can get it with booster for trackdays (fuel matters)

Edited by North London Mike

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Thanks everyone for your advice. I will try a few things, starting with different fuel and an additive, then probbaly an anti run-on valve.

 

I will report back

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Thanks everyone for your advice. I will try a few things, starting with different fuel and an additive, then probbaly an anti run-on valve.

 

I will report back

 

 

 

I'm not sure you need to spend a lot of money on branded high octane fuels.

According to my mate (A pro in the classic car rally game who looked into fuel quality and additives), one of the better petrols is ..... surpise surpise...... Tesco high Octane. He was as surpised as anyone by his findings. It turns out that Tesco have made sure they do not have any more bad press and costs about fuel..... whatever I use it all the time and have no problems, and appreciate the high octane and relatively low cost. (Mty car is newly converted unleaded head, new carbs, otherwise bog standard plain vanilla 4 and no connection to Tesco)

 

 

Mike

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Since turning to the higher Octane fuel ( and Shell by choice ) I have had no run ons. Mind you, the car has also been set up on a rolling road. In the old says and before all the mods and the rebuild it used to run on all the time and I had resorted to the clutch slip turn off.

Try the fuel first, but have you had the car set up after your engine mods?

Edited by 4Mal

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